1. Field of the Invention
The present invention relates to a communication apparatus accommodating a plurality of communication lines and terminal devices, capable of responding to an incoming and making an outgoing call to any desired person through the communication line.
2. Prior Art
In a conventional communication apparatus, i.e. a telephone exchange system, there are two options in the case where one makes a telephone call from an extension telephone: manual selection or automatic selection of the outside line. That is, a telephone user either one of plural outside line buttons and pushes it down, the user additionally dials "0" before the telephone number so that an unoccupied outside line is automatically selected or the unoccupied line is automatically selected when the handset is picked up.
In either manual or automatic selection, when there is a conflict between an incoming call and the outgoing call, the incoming call from the third party is given priority over the outgoing call to the second party. Therefore, in this case, there is the drawback that the first party must respond to the incoming call from the third party regardless of whether or not he/she wishes to. Accordingly, the third party who also could not speak with the desired person is displeased, while the first party who was going to make a telephone call from the extension telephone apparatus has to redial in order to call the second party. This is a troublesome operation and is another drawback in the conventional telephone exchange system.
Further, in a key telephone apparatus capable of accommodating a plurality of outside lines and extension telephones, the outside line buttons correspond exactly to each outside line channel, i.e., the outside line button 1 corresponds to channel B1 and the outside line button 2 to B2 of the ISDN (Integrated Services Digital Network).
However, there is another drawback in the above mentioned key telephone apparatus such that the outgoing call from the first party cannot go through from the outside line button 1 in the case where the incoming call from the third party is designated for channel B1. That is, when the outgoing call of the first party is made from the extension telephone apparatus, since the dial signal is transmitted after the telephone number is inputted and a start key is depressed, there is the drawback that the outgoing call from the first party is interrupted when the incoming call from the third party arrives while the telephone number is being inputted.